Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...

With recent viewing conditions only fair and, the scarcity of sunspots, more time was directed towards construction as detailed here.
An enjoyable, yet tedious task in this project, was the construction of the DEC bearing blocks. Commercial pillow or flange blocks are ugly and often bulky. For both cosmetic and functional reasons, I chose to make my own as shown in the following images. Those with an interest in machining may find them to be of interest.
Image 1: lengths of 3.5” aluminum flat were cut in both ½ inch and 3/8 inch thickness.
Image 2: these pieces allow for a “sandwich” block where the ½” piece is in the middle – total thickness is 1.25”
Image 3: the sides and ends of all six pieces were milled square and to precise dimensions.
Image 4: the “stack” of plates were clamped together and a series of holes drilled in a semi-circular array.
Image 5: here, one can see the scribed layout on the left plate, the countersunk holes on the back plate and, the middle plate in which the holes have been tapped #10 x 24. Note the extra space (1/8”) between the two halves to allow for the band saw kerf and some final facing off.
Image 6: with the plates screwed together, ¼” holes were drilled to serve as clamping screws for the eventual two halves of the block.
Image 7: here the plates combined into a block, are divided into two parts.
Image 8: the mating surfaces of the the two halves are faced off to a perfectly flat surface.
Image 9: the bottom half of the assembly has its holes tapped to ¼ x 20
Image 10: the two halves are now bolted together (refer image 6) and centered on a 4 jaw chuck using a “wobbler”. Noteworthy was the placement of 0.020” shim between the block halves such that following boring for the bearing, the bearing can be firmly clamped in place.
Image 11: starting with a pilot bit, a series of holes are drilled with increasing sizes up to 1: diameter. Though not shown, the hole is bored out full depth to 1.25”.
Image 12: with the outer plate removed, a 2” diameter hole is bored in the ½” plate to receive the 1” bearing which has a 2” outer diameter.
Image 13: also not shown, was the milling of a shoulder on the block base with the final result shown here. This will allow for the block to fit in the end of the rectangular steel tube of the fork arm. Here, a grove is milled in the base since the rectangular tubing has a small welding bead on the inside.
Image 14: here, a 1” end mill is used to champher the top corner of the block.
Image 15: now, it should all make sense. The two block halves can be seen with the seat for the 1” bearing.
Image 16: this image shows dry fitting of the block in the fork arm end as well as the 1” diameter shaft which fitted in both ends without any binding – thus nicely aligned.
Image 17: the close-up view shows the finished block installed in the fork arm as well as the bearing in place.

The following images show the completed, though without its drive belt, drive mechanism. It seems that the standard un-reinforced polyurethane belts die in the tropical climate so, am now working on a system to make my own custom fibre reinforced rubber belts.

Image 1: this is the South end of the mechanism showing the stepper motor, worm gear, gear train and finally the driving roller on the right with passive roller on the left. The release lever on the left, with its red knob, passes through an opening in the West pedestal panel and, allows for hand slewing. Image 3 provides a little more detail.
Image 2: this image shows the North end of the drive mechanism and in particular, the spring float mechanism for the roller base. With the belt installed, these will engage a machined flat pulley on the 1.75” precision ground RA shaft.

Having completed the welded steel fork, painted it and machined the DEC bearing blocks, it was time to put it all together. Although the OTA has yet to add its contribution to the cantilevered weight (estimated to be 55 to 60 lbs.), the 18 lb. fork and 5 lbs. of bearing blocks performed superbly. There is sufficient inertia in the system to counter vibrations yet, smoothness of rotation in both axes. Ultimately when properly balanced, I expect everything to move well with minimal effort via the stepper motor belt drive system
Image 1: this shows the completed fork assembly with a 1” diameter precision ground steel rod passing through both DEC bearing blocks. No problem with alignment as the rod spun effortlessly.
Image 2: here one can see inside the pedestal which contains the power supply and, eventually the Arduino stepper controller, etc. A stick-on/battery operated LED lite is attached to the inside East pedestal panel. The painted belt drive system can be seen with its NEMA 17 stepper motor installed. It has a holding torque of 83.6 oz/inches and, with the subsequent gear reduction will provide more than enough driving torque. The stainless steel roller bearings supporting the RA axis drum can be seen beyond the drive system and each roller is fitted with a pair of bearings at each end for a total of four each.
Image 3: the fork has been bolted to the RA shaft with a ½” stainless steel bolt as well as 6 additional ¼” bolts from the inside of the drum into the steel base plate which was welded to the fork base. The potential space between these surfaces will allow for shims during the final laser beam guided alignment – more on that later.
Images 4 & 5: these images simply show the whole structure from either end. The plastic wrap and red elastic bands on the fork arms are there to prevent my leaving grubby finger prints/smears on the painted surface.

SN12bearing - fork .jpg (296.77 KiB) Viewed 4275 times

Overall, the fork is free of any play, moves easily and, has a feeling of solidness. Just needs to be aligned now.

This is a superb piece of engineering Bill, and a pleasure to watch and read it's well documented build Really looking forward to the granulation you'll get with with the finished project when you get it pointing at the sun.

Incidentally, do you have any information on the whereabouts of Art Whipple ? He had built a 14" Solar Newton in, I believe, the early 2000's. I'd corresponded with Christian Viladrich, who has a 12" Solar Newton, to see if any other such similar sized scopes exist. As such, Christian and I would share second place for the largest Solar Newton's in the world.

Why do I raise this question ? Our fledgling University will want to get some local media publicity on my scope and, media folks seem obsessed with such questions as, "Is it the biggest in the World ?" I'll need some answers.

Now, for some creative fun. Notwithstanding the best efforts to carefully measure twice, to check diagonals for square or set up pieces in jigs, errors will occur and, often compound rather than cancelling each other out. With the fork mounted on the North drum roller and RA shaft, the question remains – “Is everything concentric ?". Probably not.

To deal with this, one needs a poor man’s “theodolite” as shown below. This “device” allows for mounting a standard laser collimator on a frame such that it can tilt up or down, slide up or down and rotate upon a vertical axis.

Align1 2.jpg (584.21 KiB) Viewed 4109 times

The “device” was then mounted on a sturdy tripod from a previous telescope build and, lined up in front of the new Solar Newtonian fork. Note also the white cardboard square mounted on the rear RA shaft bearing mount. It has a vertical line on it and works on the same principle as marine navigation using range lights or lights-in-line.

Align2.jpg (248.57 KiB) Viewed 4109 times

The tripod bearing the device is positioned such that laser beam rests on the line. Then the laser is tilted downwards such that the laser spot lands on the ½” hex bolt at the fork base which has a center mark. With a little fiddling and moving about, a tripod position can be found where the laser spot will intersect both the line and the center of the hex bolt. This now defines a vertical plane representative of the middle of the RA shaft. Knowing the angle of the RA shaft to horizontal, the laser collimator can be tilted to an equivalent angle and moved down to center on the hex bolt center. With a length of ½” plywood attached to the front of the DEC bearing blocks, one can mark out the center, drill a 1” hole and cover it with a small piece of glass with cross hairs inscribed. We have thus created 3 points in space on the laser beam.

If all is well, the laser spot should intersect the cross hairs as well as the center of the hex bolt in the next image. As luck would have it, they intersected perfectly. However, when the fork was turned on the RA axis, the spot wandered about within a 3/16” circle. Not bad for a first try but simple trigonometric calculations will demonstrate that a 1/8” error translates into 0.3672 degrees off-axis. Given the solar disc subtended angle of 0.53 degrees, further refinement is needed.

Align3.jpg (178.36 KiB) Viewed 4109 times

Align4.jpg (183.65 KiB) Viewed 4109 times

Recall that the ½” thick aluminum face of the front bearing drum has 6 - ¼” holes which register with ¼ X 20 tapped holes in the 1/4” steel plate which is welded to the base of the fork. Screws in these holes can be accessed from the rear as shown. Thus, with loosening and placement of shims in the potential space between the steel plate and drum face, minor adjustment in alignment can be had guided by the position of the laser spot.

Align5 3.jpg (111.38 KiB) Viewed 4109 times

Align5 2.jpg (234.29 KiB) Viewed 4109 times

A more sophisticated option is to drill holes near the other six in the aluminum front bearing plate. These would be tapped 10 X 24 but no matching holes would be drilled in the steel plate. With ¾” – 10 X 24 screws fitted in these holes and accessible from the rear, one could play them against the ¼” screws ie: tightening the 10 X 24 screw would widen the gap and tightening the ¼ X 20 screw would lock the position, to allow for very fine adjustment. For example, a ¼ turn would result in advancing the plate 0.0104” This is the course I plan to follow tomorrow.

Do hope that my description is not too confusing. It all makes sense to me but, I’d be interested on constructive commentary in case I’ve gone astray in my logic.

Good logic there Bill. After contemplating over 2 cups of coffee this morning, the only thing I could think of is how do you know the plywood used is completely square / true? The plywood we have in our workshop can be bowed sometimes. Not saying yours is, just thinking out loud. Saying that, you have adjustment so even if there is small error it can be counteracted.

Thanks for your response. True, they don't make plywood like they used to do - most of the current crop is warped/twisted and full of voids. Fortunately for this project, I had some good quality 12mm 8 ply birch plywood. Not quite marine grade but, close.

One issue that I've yet to resolve is whether the fine tuning will be preserved once the OTA and its weight are added to the fork. Will then need an alternative method to confirm concentricity. Likely, with DEC set to 90 degrees ie: parallel to RA axis, and focused on an object, simply rotating on the RA axis should work.

Since there may have been some confusion in my last post regarding alignment with push/pull screws in the drum, here's an exploded image to clarify. The 1/4" steel plate welded to the fork base has six 1/4 X 20 tapped holes for the larger screws passing through the 1/2" aluminum front plate. Smaller 10 X 24 screws pass through tapped holes in the 1/2" aluminum plate but, there are no matching holes in the 1/4" steel plate.

Explode.jpg (222.62 KiB) Viewed 4072 times

Thus, when assembled, one has access to all of the screw through the rear of the drum. The smaller screws can be used to make fine adjustments in the space between the plates and, the larger screw will lock all in place. Finally, a 1/2" hex bolt passes through the fork base into the RA shaft.

With the paucity of sunspots until recently, more time was spent in the shop making bits’n’pieces. Here, attention was directed towards the DEC drive system where, I chose a tangent arm design. Since the scope is exclusively for solar imaging, the range of movement through the celestial sphere is quite narrow. A tangent arm would be less complicated and less expensive to build. The first image panel shows the completed device and some close up details. It will be mounted on the West arm of the fork with the clamping end fitted to the DEC axis trunnion and, the motor/leadscrew portion fixed the the fork arm. It won’t be installed until the OTA is added to the mount. Here are some comments on the numbered images: - apologies for starting with the larger numbers first - it’s been a long day.

TArm2.jpg (340.97 KiB) Viewed 3804 times

8> this image shows the entire tangent arm with the DEC axis clamp on the left and the motorized leadscrew on the left.
9> this is the clamp end where the knurled knob compresses the head - best seen in the following image. The black plastic knob screws into a 1/2” X 20 tpi threads in the trunnion end. With both loosened, one can hand slew the OTA. When both are tightened, the tangent arm takes over.
10> this is the inside portion showing the socket for the the 1” DEC trunnion.
11> at the fixed motorized/leadscrew end, one can see the bronze half nuts which move up/down in the arm to allow for the changing radius when in use. The leadscrew is a stainless steel 1/2” X 20 tpi threaded rod seated in bronze bearings at either end.
12> in this image, the half nuts are opened for quick change of position.
13> the opposite end shows the cover over the gear train driven by a NEMA 17 size stepper motor. The motor will be driven by an Arduino and Adafruit motor shield v2.3
14> with the cover removed, one can see the gear train with a reduction of 0.42 X’s.

The following panel shows some of the machining steps - described as follow:

TArm1.jpg (305.45 KiB) Viewed 3804 times

1> here 2 pieces of hexagonal bronze material are clamped together and registration holes drilled.
2> the next step was to bore an opening for the eventual leadscrew prior to threading.
3> completed and separated, one can see the 2 small roll pins for registration and the 1/2 X 20 tpi threads cut with the leadscrew in the background.
4> here the DEC axis clamping end is being bored to 1”.
5> a slot is now being milled into the clamp for fitting of the arm itself.
6> here, a slot is being milled into the arms at the leadscrew end to capture the bronze half nuts and allow them to move in/out. (refer images 11-14 above)
7> finally, a slot was made in the clamp end for locking. (refer image 10 above)

Often, I’m asked, “when will it be finished ?” This project is not unlike building an house. With the walls, roof up and windows, doors installed, one might think it is almost finished. “Nyet”, remember the house still needs wiring, fixtures, plumbing, interior walls, painting, flooring, cabinets, etc. Much the same here as the “yet to do” list includes the following: install, the OTA, install the tangent arm, fit eyepiece holder and filters in draw tube, fit secondary mirror, strip primary mirror, machine and install an RA locking mechanism, install and wire electronics with lead to remote pad, install mirror, align, balance amongst other miscellaneous tasks.

One significant issue is that of the belts for the RA axis drive. Originally deigned to use endless polyurethane belts, I discovered that they fall apart in the tropics when under any load. The alternative will be fabric reinforced rubber belts but custom sizes are hard to come by. Thus, I’ll have to set up a process to make my own - quite doable with a little effort.

The first order of the day was to revise the tangent arm mechanism on the DEC axis. The original design failed to grip the trunnion adequately so, a revised version consisting of two 3 ½ inch plates were machined for the trunnion. The inner one was fixed to the trunnion whilst, the outer plate (also part of the arm) would be clamped to the trunnion/plate system with a sandwich of special rubber disc used by studios to lock boom lights in place. The first panel shows some of the machining involved whilst, the second shows the finished system with a close-up of the stepper motor driven lead screw.

DEC brake.jpg (673.78 KiB) Viewed 3389 times

Tang drive.jpg (408.03 KiB) Viewed 3389 times

Next, it was time to take the plunge and strip the mirror. I used Gordon Waite’s method referred to earlier as a YouTube video. The following panel shows the untreated mirror in a plastic lined tray since the ferric chloride used as an etchant stains everything in sight. Duck Tape is placed around the mirror’s circumference with ½” proud above. The ferric chloride is poured over the mirror which is then gently rocked/agitated much as one would do when developing a print in the darkroom. Within 10 minutes, one could see the etchant eating away the aluminized coating (as well as the quartz over-coating) . Within 30 minutes the stripping was completed though, I allowed another 15 minutes for good luck. In the last frame, one can see right through the mirror. The ferric chloride was removed and the mirror thoroughly rinsed in clean water.

Mirror strip.jpg (713.13 KiB) Viewed 3389 times

The mirror was then fitted into its mirror cell (also provided by Agena Astro as part of their GSO mirror and mirror cell products – for U$110, it was cheaper to buy then make. With the protective cover applied, the whole assembly was then carefully mounted in the OTA.

Mirror done.jpg (136.5 KiB) Viewed 3389 times

The next panel provides 3 views of the whole scope with the OTA mounted. Everything moves smoothly with minimal vibration. The GSO focuser has yet to be added and will require more weight at the bottom for balance. Pointed to the Zenith, the maximum height is 71”.

SN12 scpe.jpg (1.06 MiB) Viewed 3389 times

The scope’s home position is seen in the next panel. Maximum height is 49”. The final image shows the RA axis locking mechanism withe locking knob indicated by the arrow.

Scope home.jpg (481.43 KiB) Viewed 3389 times

RA lock.jpg (237.39 KiB) Viewed 3389 times

What’s next ? Balancing the scope, completing the Arduino electronics and remote control and, making the drive belt. So, not quite finished yet. Lots yet to do. It has seem a fun project though.

Very much enjoyed Bill with such precision to detail.Not only a great piece of engineering but I would go as far to say an artistic masterpiece in many respects.I also found your adjustment setup for the drum roller very informative as I am often performing various adjustments on bits and pieces in my Honey extraction plant so always good to see something that may be helpful in future adjustments.
Regards Derek.

Thanks Derek and Mark. Progress had slowed a bit recently but, hope to carry on. Aside from final balancing, have yet to fabricate a suitable belt for the drive system and complete the Arduino electronics/remote when my student Intern returns in May.

My 12” Solar Newton found itself on the back burner during the last few months owing to several other commitments. Nonetheless, some progress has been made as will be seen in this post. Apologies for the quality of the images - they were simple snaps with my iPhone

First, the GSO focuser has been installed complete with one of my DIY remote focusers which drives the fine focus knob.

12SN1.jpg (174.67 KiB) Viewed 2050 times

Balancing came next and, a 7lb. lead casting was made for the OTA bottom end. By casting, I mean that lead shot was obtained, mixed into a “soup” of fibre glass resin and cast in a premade, disposable mold. It was positioned on the opposite side of the focuser given the focuser weight plus the 2” 4X TeleVue Power Mate which weighs a ton.

12SN2.jpg (79.68 KiB) Viewed 2050 times

The DEC axis uses a tangent arm driven by a stepper motor through a ½” x 10 tpi lead screw. The arm has been reinforced with a steel 3/8” rod bent in a tight “V”. The gear train off the stepper motor has been disengaged.

12SN3.jpg (128.02 KiB) Viewed 2050 times

12SN4.jpg (177.44 KiB) Viewed 2050 times

The polar axis is driven by second stepper motor through a gear train and belt system. The gear/belt ratio works out to 1:2429 – a little less than the ideal 1:1440 going from 1 rpm to 1 rev/day. Thus, the input speed of the stepper works out to 2429/1440 = 1.687 rpm. With ½ stepping, this will require 11.247 pulses/sec. The rust on the PA shaft is part of living in the tropics - it will be cleaned off and oiled in the future.

The white drive belt can be clearly seen as well as the gear train. The idler roller in the drive has a small crown to keep the belt inline. The lever with the red knob on the drive mechanism allows for disengaging the drive so that the OTA can be hand slewed.

12SN56.jpg (281.15 KiB) Viewed 2050 times

12SN78.jpg (256.84 KiB) Viewed 2050 times

I make no claim to proficiency in electronics but fortunately, have an electronics engineer friend (David Brown) and a very bright student intern (Shannon Williams) who have been a very helpful. Using an Arduino uno R3 and Adafruit stepper motor shield, they created the circuit below.as well as the C++ code. The boards will sit adjacent to the 12 volt regulated power supply in the base. The rear plate of the base enclosure has a female/female gender changer installed. The control box cable is a 16 ft. SVGA cable male/male. Thus, rather than driving one’s self nuts by attempting to solder 24 ga. wire into the pin cups of the plug, I simply took the SVGA cable and cut one end off by 15” such that both plugs would mate with the panel female/female gender changer and the other wire ends could be tinned and fitted to a breadboard and connections in the control box. Still debating whether to leave the breadboard in place rather than hard-wire all the connections. The smaller CB with DRO is a voltage converter allowing for lower output if needed. The red/green LED's in the breadboard represent the stepper motor coils.

12SN9.jpg (222.77 KiB) Viewed 2050 times

Image10.jpg (209.94 KiB) Viewed 2050 times

The Control box separates DEC and RA controls. Each is bidirectional and, for DEC speed a potentiometer is used for speed control whilst for the RA speed, the default is one rev/day with several multiples of higher speed for positioning. The yellow gender changer will be fitted on the base rear plate.

12SN11.jpg (225.1 KiB) Viewed 2050 times

The soldering will begin soon and hopefully, it will run as designed. By the time I get this all finished, there may be no sunspots.

My 12" Solar Newton has fallen behind given a number of circumstances. Although the finders have been fabricated and attached, the Arduino /stepper motors setup, the Arduino code needs some tweaking and calibration.

The following images are self-explanatory.

finders.jpg (236.81 KiB) Viewed 1384 times

base.jpg (116.93 KiB) Viewed 1384 times

arduino.jpg (183.55 KiB) Viewed 1384 times

More significantly, health problems have also intervened and, a diagnosis of esophageal adenocarcinoma has presented itself. Survival times at this stage are measured in single digit months not years.

Thus, in the next few months, the beast will not likely reach first light and there will be no further images from my 8" Solar Newton.

Over the last few years, I've enjoyed participating in the forum and, wish it and its members all the best in the future.